Electrolytic deposition of manganese



' Patented A 25, 1944 UNITED STATES PATENT orncs morn/or. onsrosmon orPaul II.

.ccmrationoflllineis No Drawing. Application May 81'. 1989. Serial'lio.210."!

a m (or. 204-105) ganese sodium citrate. manganese acetate and othermanganese salts has heretofore been proposed. The aqueous electrolyteshave utilized as such or in coniunction with addition 'agents suchasammonium salts and ethanolamine salts, for example, ammonium sulphate,monoethanolamine sulphate, triethanolamine sulphate, and the like. Inaddition. the prior art suggested the preliminary purification of theaqueous manganese electrolytes by various 188th. ods. Despite all ofthese efforts to produce fully satisfactory depositions; no one hasheretofore successfully produced satisfactorily thick deposits which aresubstantially free from sulphur. Thus. for example, while good depositshave been reported in connection with the process described in UnitedStates Patent No. 2,119,560, the sulphur content of the depositedmanganese has ranged from about 0.2% to about 0.8%, repre- :BlqtBtU/Cdeposits containing of the order of The present invention is based uponnew discoveries which enable the formation of exceptionally satisfactorydeposits of manganese, of seed thickness, and of substantial freedomfrom sulphur. In general, these" results are obtained by the utilisationof novel methods of purification of manganese electrolyte solutionscoupled with proper control of current density and manganese content ofthe catholyte.

Aqueous catholyte solutions which are employed in the pmdubtion ofelectrolytic mangan'ese usually contain relatively large amounts ofmanganese salts and ammonium salts or salts of organic nitrogenous basesor the like, an illustrative. example being of the order of 70 grams of'manganese sulphate and 200 grams'ol ammonium sulphate per liter as msiorconstituents. However, the electrolyte also usually contains smallamounts of salts of one or more of the elements iron, nickel, cobalt,molybdenum, vanadium, arsenic, copper, zinc, and lead. These impuritiesseriously interfere with the production of satisfactory deposits ofhigh-purity electrolytic manganese.

In accordance with the present invention, the principal step ofpurifying the electrolyte is accomplished by the utilization of asulphide ion to effect precipitation of nickel, cobalt, copper and zinc,the substantial removal of these metals be- Ambrose, Ooilese was, as.asllsnor a Development Oompanr. Ghieaso. ill a ing apparentlypkrticuiarly essential if manganese deposits of and density andsubstantial freedom from sulphur are to be obtained. While these metalsare effectively removed in accordance with the practice of my invention,other heavy metals are. likewise at least substantially.

eliminated.

-It has been found that when a sulphide ion is added. for example, to anaqueous solution of manganese sulphate containina' traces of nickel andcobalt and havin: a hydrogen ion concentration greater than about 6.0,pink manganese sulphide and other heavy metal sulphides are essentiallyprecipitated. If filtration to remove such precipitates is carried outunder these conditions, it has been found that the filtrate will not beentirely free of nickel and cobalt. If. however, the solutionispermitted to stand for a substantial period of time. at least one hourand preferably several hours in the usual case, the pink manganesesulphide undergoes a change and a black precipitate containing thenickel and cobalt is formed. On filtration, under such conditions, thesolution is substantially free from nickel and cobalt.

While good results are obtained by following the proceduredescribedhereinabove. so far as the initial purification-step isconcerned. it has been found that further improvements result from theaddition to the electrolyte of a finely divided-material such asinfusorial earth. trlpoli, activated charcoal, alumina, silica gel,barium sulphate, titanium dioxide, or anyother inert material presentinga large surface. This sur fees may be produced in other ways, forexample. as by forming a=precipitate in the solution itself. forexample, by adding barium sulphide thereto. Ex ptionally/satisfactoryresults are obtained by the use of activated charcoal and it ispreferred,

therefore, to employ this material. The activated charcoal or the likereduces materially the length of time that the precipitate of pinkmanganese sulphide and other heavy metal sulphides is required to beallowed to stand.- Thus, for example, instead of requiring upwardly ofan hour and in numerous cases several hours, the addition of activatedcharcoallor the like reduces the time of standing to only a few minutes,in most instances, to approximately 10 or 15 minutes.

In order to obtain highly pure deposits of electrolytic manganese ofdesired density, the anode current density should be below twentyamperes per square foot and, for best results, between about sixteen andabout eighteen amperes per square foot. Furthermore, the manganesecontent during electrolysis should be about fifteen grams per liter. Inorder to accomplish this result, for example. electrolyte containing atleast about twenty-five grams per liter of metallic manganese asmanganese sulphate may be passed through the cathode compartment at sucha rate that the solution leaving the cathode compartment contains of theorder oi ten grams of metallic manganese as manganese sulphate perliter. Separate anolyte and catholyte circuits are maintained and theymay be separatedby a relatively impermeable diaphragm it it is notdesired to make large amounts oi manganese dioxide at the anode.

The following example is illustrative of the practice of my invention.It will be understood that variations may be made with respect to themanganese salt to be electrolyaed, the character of the addition agentor agents, the nature of the cathodes and anodes, current densities andthe like, as well as in other ways, all within the scope of theinvention in the light oi the guiding principles which have beendescribed in detail hereinabove.

'I'o 10,000 liters of an aqueous solution containing 150" grams ofammonium sulphate and 35 grams of metallic manganese as manganesesulphate per liter, said solution containing traces of nickel, iron andcobalt, one pound of colorless ammonium sulphide and one pound ofactivated charcoal were added. The solution was stirred and then allowedto standior 15 minutes. The solution was then filtered-through a highsilicon iron filter press using an ordinary filter cloth. The resultingsolution was free from nickel and cobalt as indicated by tests withdirnethylglyoxime and alpha nitroso beta naphthol. It is particularlypreferred that the pH of the solution be maintained between 'i and 8although good results may be obtained employing a pH of about 5.5 andabout 0.5. The resulting solution is then electrolyzed in'a lead linedcell with a heavy canvas diaphragm, sheet steel cathodes and leadanodes, the anode current density utilized being approximately 18amperes per square foot.

Instead of employing ammonium sulphide,

' other sulphides may be utilized, it being immaterial in what form thesulphide ion is added. Ammonium sulphide, hydrogen sulphide and bariumsulphide are particularly preferred because they do not contaminate thesolution. It will be understood that the final, purified solution whichis to be electrolyzed, when prepared in accordance with the presentinvention, contains only the amount oi sulphide ion represented by thesolubility of manganese sulphide in the particular electrolyte utilized.In general, the sulphide ion is employed in amounts less than or notsubstantially in excess of, about 1% of the stoichiometric equivalent ofthe manganese present.

While the practice of the process may be carried out with solutionscontaining only manganese salts such as manganese sulphate, it isdistlnctly preferable to employ aqueous electrolytes containing not onlymanganese salts but also addition agents such as ammonium salts, forexample, ammonium sulphate as well as salts of alkylolamines and relatedcompounds. Where ammonium sulphate is utilized, together with manganesesulphate, there should be present at least about 100 grams of ammoniumsulphate per liter oi electrolyte solution in order to obtain the mostsatisfactory results. a

What I claim as new and desire to protect b Letters Patent oi the UnitedStates is:

1. In a method of making high purity manganese which compriseselectrolyaing an aqueouesolution containing a soluble manganese seems:

salt, the steps which comprise adding to said aqueous solution asulphide ion and an inert. solid material having a. high specificsurface, the sulphide ion being efiective to precipitate such heavymetals as may be present, allowing the solution to stand for a shortperiod of time, and filtering.

2. The method defined in claim 1 wherein the ineil't, solid materialcomprises activated charcoa 3, The method defined in claim 1 wherein theinert, solid material is activated charcoal, the sulphide ion added isin an amount less than about 1% oi the stoichiometric equivalent oi themanganese present, the activated charcoal being employed in amounts atleast equal to the weight of the added sulphide ion.

4. In a process oi producing electro tic manganese which compriseseleetrolyzing aqueous solution 01' manganese sulphate, the whichcomprise adding a member selected from the group consisting of ammoniumsulphide, hydrogen sulphide, and barium sulphide to said aqueoussolution to precipitate such heavy metals as may be present, adding afinely divided inert material to the solution, allowing the solution tostand for at least about 10 minutes, and then filtering the solution.

5. The process defined in claim 4 wherein the aqueous solution ofmanganese sulphate contains a substantial content oi ammonium sulphate.

6. In a method of producing electrolytic manganese of high purity whichcomprises electrolyzing an aqueous solution containing at least 15 gramsoi manganese as manganese sulphate and at least grams of ammoniumsulphate per liter of solution by utilizing an insoluble anode and ananode current density between about 16 and about 20 ampers per squarefoot, adding ammonium sulphide to said aqueous solution in amounts notsubstantially in excess of 1% of the stoichiometric equivalent or themanganese present, adding a finely divided inert material to thesolution, allowing the solution to stand for at least several minutes.and filtering.

I. In a process of producing electrolytic manganese by electrolysis ofaqueous solutions of manganese sulphate containing substantialproportions of ammonium sulphate, the steps which comprise adding asulphide ion to said solutions at a pH between about 7.0 and 8.0, addingactivated charcoal, allowing the solution to stand for an appreciableperiod of time, and filtering to remove the precipitated sulphides ofsuch heavy metal impurities which may be present.

8. The method 01 claim 7 wherein the sulphide ion is incorporatedthrough the addition oi a member selected from the group consisting ofhydrogen sulphide, ammonium sulphide and barium sulphide.

9. The method of claim 7 wherein the sulphide ion is incorporatedthrough the medium of ammonium sulphide and the filtrate is electrolyzedutilizing an insoluble anode and an anode current density between about16 amperes and about 20 amperes per square foot, the electrolysis beingeiiected in a diaphragm cell and the manganese electrolyte beingcontinuously circulated through the cathode compartment at such a ratethat there is always present therein at least about 15 grams oimanganese as manganese sulphate per liter.

PAUL M. AMBROSE.

